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The 2 seminars this past week in Denver reguarding Safety and Proper Distilling Techniques were extremely eye-opening. thanks to ADI and the participants for sharing their experiences and input. One aspect reguarding ethanol vapor and potential for explosion/ flash fire that was not really discussed was barrel aging. We are building a Rum distillery. My plan is to have barell storage on the 2nd floor in a room isolated from our still. The (newly discovered) problem is that the barrel storage is in proximity to our boiler. I plan to age the rum at about 55-60% abv. How volatile is vapor from evaporation (at this abv %)? Is firewalling off the boiler enough, or do I need to consider moving the boiler (yes, it's already installed and partially plumbed in). There is a fan (not explosion proof) to move vapor from the area. Nothing in this room is explosion proof (lights, heaters, lift). I plan to look into 'Ethanol Vapor Detectors', but outside of that, what are your opinions. Any input will be GREATLY appreciated.

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They were rather excellent and eye opening seminars. My plans were changed (we'll be now arranging for a boiler cutoff on cooling water failure, among other things. Luckily, we were already designing with safety in mind.) We're planning on the boiler being firewalled, but that firewall will be near barrel storage so let's do these calcs for my sense of well being.

On the barrels, if we take 2% per year as a notional number for evaporation, and assume it to be purely EtOH (it won't be). We can calculate Barrel Vapor per hour per Barrel

53 Gal * 0.02 = 1.06 Gal / Year

1.06 Gal / 8760 H/ hear = .000121 Gal/hour

now, I trained as a chemist, so I prefer metric, so

0.00021 * 3.785 = 0.000458L or 0.458 mL per Bbl per Hour.

I'm making an assumption about %by volume, which how LEL are shown. (chemists can mean all sorts of things by %, and I was an analytical protein chemist, so this is out of my expertise). I'll assume volume of pure gas at stp / volume of space. So let's get the volume of the Ethanol.

First we need the mass of EtOH: 0.458 mL * 0.789 g/mL = .361 g EtOH

Next we need moles of EtOH 0.361g / 46.07 g/mol = .00784 mol EtOH

One mole of an ideal gas at STP occupies 22.4L (just a fact)

0.00784 mol * 22.4L / mol = 0.176 L So that's volume EtOH per Bbl per Hour.

Now the LEL for EtOH is 3.3%. Can we take from that how much space the room would need to have to be under LEL? I think we can.

0.176L / 0.033 = 5.33 L. That's the space at which the amount of EtOH coming off a single barrel in one hour would be restricted to to be at LEL for Ethanol.

Awfully small space. Awfully small amount of ethanol. Your room will have many liters. (A cubic meter is 1000L).

Assuming some air exchange and reasonable breathing space, I don't think you can get to LEL from just angel's share. I'd worry much more about vapor from dilution if you dilute in that space. In normal circumstances you probably won't get to LEL, but as Max pointed out, abnormal circumstances happen. Mitigate that risk. Treat the space as having potential vapor hazard, with alarms and proper explosion proof equipment.

NB: I'm not a safety expert, I'm just explaining the math. PLEASE, SOMEONE CORRECT ME IF I'M WRONG. [EDIT: AND THEY DID CORRECT ME. See Max's response, and if the angel's share is highter then you'd expect that will increase the amount as well.]

To finish the calculations, you will need:

1. The volume of the barrel storage (not counting the barrel volume, which will not be negligible).

2. Air exchange. (if 4 exchanges per hour, divide by 4)

3. Number of Barrels stored (multiply by number of barrels)

Of course, as an analytical chemist, I would, if I needed this number accurately, measure it. (I don't know what the test method is). This is just a back of the envelope calculation which gives you the order of magnitude for just the angel's share. I assumed EtOH to be ideal (it probably isn't), STP ( we usually don't keep rooms at 25C any more), %EtOH of Angel's share to be 100, Angel's share to be 2%/year, and evaporation rate to be constant (it won't be). So it's just an estimate.

Chuck Burkins

Edited by burk
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I think I follow your math, but isn't the angel's share typically much higher? I thought it was 10% or more if you're using smaller barrels. Of course, the % of ethanol in the angel's share will fluctuate.

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I think your conclusion could be misleading to some and, perhaps even potentially dangerous. It seems you're assuming the ethanol vapor will mix homogenously with the entire volume of the room, and your assumption of 4 air exhanges per hour sounds way too high to me.

I'll just assume your math is in the ballpark for the vapor. So if you say 5.33 L/hr per barrel, that's 4.5 cubic feet of explosive vapor per day. Who has just one barrel? That's 450 cubic feet of explosive vapor for someone that's got 100 barrels in storage. Since ethanol vapor is heavier than air, it will tend to collect at floor level if there isn't a lot of air turbulance to mix it up. Let's now assume that same distiller has a 2500 sqft warehouse. In one day their barrels could create a deadly layer of ethanol a couple inches deep at floor level- right where pumps, compressors, and extension cords are located. What about over a 3 day weekend? Or maybe the distiller locks up tight and goes on vacation for two weeks in the middle of summer when it's nice and hot out? I could see a lot of vapor building up in that time, and even if it is only a 2% average annual barrel loss I'm sure the rate is proportionally much higher in summer than winter. Your numbers would double if it's 4% per year in August.

One remedy, as you hinted at, is air exchange. But I certainly wouldn't treat that as an assumption. Who really has 4 exchanges per hour? Let's assume our distiller's warehouse has 20' ceilings. That's 50,000 cubic feet of space At my warehouse I have a really big (and noisy) exhaust system capable of venting 3600 cfms. Maybe that's ~4 theoretical exchanges per hour if our distiller had a similar system, but again we can't expect perfect mixing of the air, especially if the vent system is above floor level. And even then, who really leaves their exhaust system running 24/7? I'm willing to admit I don't. It's simply not practical to heat and cool that much fresh air. However I don' t have a lot lof barrel storage, and I do have an electronic vapor detector (specifically calibrated to ethanol) that's connected to an alarm system.

I can just imagine a lot of scenarios where barrel vapor could create a hazardous sitauation. Maybe some of those scenarios aren't very likely, but with hundreds of distilleries out there an unlikely scenario isn't exactly that unlikely. At the very least, you should consider that barrels will contribute to your overall vapor load, in combination with all your other activities with potential vapor leaks.

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One more scenario-

Our distiller is aware of potential vapors from his barrels, and decides to build a small storage room separated from the rest of the warehouse with fire-rated walls and doors. Concerned with 100 barrels enclosed in such a small space, our distiller adds a ventilation system that runs 24/7 and specifically exhausts from the floor level.

Then one evening after work everyone in town loses power. It was really hot that day and too many people had the AC running. The power company couldn’t keep up with the demand. But that’s ok. Our distiller used up as much food from the fridge as he could, and had a big BBQ in the back yard that night and got a great night’s sleep. It wasn’t until the next morning, over 12 hours later that they got the power turned back on. It didn’t occur to the distiller that in just one warm night without power the un-vented barrel room had accumulated a couple hundred cubic feet of flammable vapor. When the power was restored the exhaust fan motor kicked back on with a little spark, as motors tend to do. Unfortunately, our distiller originally decided not to get the $3000 explosion proof fan and got a $300 Chinese model online instead. As he figured it, that exhaust was just a precautionary and redundant system anyway. He read it somewhere on the internet that you couldn’t get explosive levels of vapor from a barrel’s angel share.

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Max,

Thanks. I was hoping that someone who knew better would speak up. Real world trumps back of the envelope yet again. I worked in a field where 4 exhanges would be low. I also assumed even mixing, and I should have known better. I also didn't realize that ethanol vapor sinks. So the sensible solution like you suggest is ethanol vapor monitoring sensors.

I'm going to edit my response to suit.

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Good morning,

Sorry for being late to this discussion.

I'll start another thread today with some other information, however, here is the input from NEC via DISCUS "Recommended Protection Practices for Distilled Spirits Beverage Facilities". Long and short of it, your calculations and your approach to air exchange are exactly correct.

"In barrel warehouses, either racked or palletized, electrical equipment approved for use in a Class 1, Division 2 hazardous locations should be used throughout. Exceptions: Ordinary electrics, such as lighting fixtures, may be used when: a.) attached to the underside of the roof ----- b.) mounted beneath liquid tight floors while maintaining a minimum of 5' clearance from the barrels."

With regard air exchanges, our industry is bound to an area classification for distillery, bottling lines, and warehouse of a minimum of 5 air exchanges per hour.

Best,

John

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Thank you for any and all info so far. We would not total more that 24 barrels in this area. We now plan to firewall off the boiler, put in an explosion proof fan (which we will run continuously). The fan is in the corner of the space with the barrels lined up along the wall between an open window and the fan. I will source the fan with '5 air exchanges per hour' in mind. Ethanol vapor sensors will also be installed (calibratde in the 3.5% - 19% range). Still working on lighting and other electronics. Again, thanks to all and is there ANYTHING ELSE?

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John,

That is a useful quote. May I ask where you got that report? I'd like to take a look.

Chris

Good morning,

Sorry for being late to this discussion.

I'll start another thread today with some other information, however, here is the input from NEC via DISCUS "Recommended Protection Practices for Distilled Spirits Beverage Facilities". Long and short of it, your calculations and your approach to air exchange are exactly correct.

"In barrel warehouses, either racked or palletized, electrical equipment approved for use in a Class 1, Division 2 hazardous locations should be used throughout. Exceptions: Ordinary electrics, such as lighting fixtures, may be used when: a.) attached to the underside of the roof ----- b.) mounted beneath liquid tight floors while maintaining a minimum of 5' clearance from the barrels."

With regard air exchanges, our industry is bound to an area classification for distillery, bottling lines, and warehouse of a minimum of 5 air exchanges per hour.

Best,

John

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Check out the Beacon 110 from RKI. It's their recommended unit for ethanol. Based on my own quote several months ago, I would assume it's priced in the ballpark of $1600. But you don't want to skimp on something so critical to your life and business. Just make sure you're very explicit that you want it calibrated to ethanol. It has a different calibration than their normal hexane standard. This is for a single location. Depending on the size of your operation, you may want to inquire about upgrading that can monitor multiple locations.

http://www.rkiinstruments.com/pages/beacon110.htm

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Thanks Max.

The Beacon 110 will work but my preference would be a portable detector. It would generally stay in one place, but I'd like to be able to test different areas of the distillery every so often as part of a maintenance schedule.

Any ideas on a portable ethanol detector?

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